Forest Fuels and Fire Forest Fuels and Fire Behavior Behavior Rick Everett Rick Everett ESPM 134 ESPM 134 Spring 2008 Spring 2008
Where we’re going: Where we’re going: � Fuels: What they are Fuels: What they are � � Fuel Classes Fuel Classes � � Fuels & Fire Hazards Fuels & Fire Hazards � � Fire Behavior Fire Behavior � � Fuels, Topography, Weather Fuels, Topography, Weather � Flame & Flame front Characteristics Flame & Flame front Characteristics � Spread Characteristics Spread Characteristics � Fire Behavior Measurements Fire Behavior Measurements
Fuels Classification Fuels Classification � Natural fuels Natural fuels � From natural forest growth and death. From natural forest growth and death. � Includes all leaf and branch materials Includes all leaf and branch materials � Includes all duff, and litter Includes all duff, and litter � Activity fuels Activity fuels � Human Human- -caused caused � Logging Logging � Thinning Thinning � Herbicide Use Herbicide Use � Recreation Recreation � Dead, downed & remnant Dead, downed & remnant � All dead & down materials on the forest floor All dead & down materials on the forest floor � Can be activity or natural Can be activity or natural � Either sound or rotten Either sound or rotten
Timelag Theory Timelag Theory � Timelag Principle: wetting and drying of fuels Timelag Principle: wetting and drying of fuels � � Timelag: the amount of time required for a fuel to Timelag: the amount of time required for a fuel to reach approximately 63% of the difference between reach approximately 63% of the difference between initial moisture content and equilibrium moisture initial moisture content and equilibrium moisture q content content � The 63% is a step function solution: 1 The 63% is a step function solution: 1- -1/e = 0.63, where 1/e = 0.63, where ‘e’ is the base of the natural log. ‘e’ is the base of the natural log.
Timelag Classification Timelag Classification � The amount of fuel exposed to the atmosphere The amount of fuel exposed to the atmosphere � is related to fuel size is related to fuel size � Small diameter fuels have a large surface to area ratio Small diameter fuels have a large surface to area ratio � Change rapidly with changes in temperature and humidity � Change rapidly with changes in temperature and humidity Change rapidly with changes in temperature and humidity Change rapidly with changes in temperature and humidity � Big diameter fuels have a small surface to volume Big diameter fuels have a small surface to volume ratio ratio � Change slowly with changes in temperature and humidity Change slowly with changes in temperature and humidity � Timelag increases with increasing Fuel diameter Timelag increases with increasing Fuel diameter �
Fuel Classes Fuel Classes Classified by how quickly they can respond to changes in atmospheric Classified by how quickly they can respond to changes in atmospheric � conditions conditions � 1- -hour timelag fuels: 0.0 to 0.25” hour timelag fuels: 0.0 to 0.25” � 10 10- -hour timelag fuels: 0.25 to 1.0” hour timelag fuels: 0.25 to 1.0” � 100 100- -hour timelag fuels: 1.0 to 3.0” hour timelag fuels: 1.0 to 3.0” � 1000 1000- -hour timelag fuels: 3.0 to 8.0” hour timelag fuels: 3.0 to 8.0” Sampled using a line intercept transects (the Brown Transect Sampled using a line intercept transects (the Brown Transect Sampled using a line intercept transects (the “Brown Transect” Sampled using a line intercept transects (the “Brown Transect” � � � # of fuels intersecting 30m line can be converted to tons/unit area # of fuels intersecting 30m line can be converted to tons/unit area Usually thought of as a “% fuel moisture”: Usually thought of as a “% fuel moisture”: � � If a 1 hour fuel stick is carrying only 10% of what is its tested maxima for If a 1 hour fuel stick is carrying only 10% of what is its tested maxima for moisture, then the % fuel moisture is 10% moisture, then the % fuel moisture is 10% � Easy to test, 0 Easy to test, 0- -100% scale 100% scale � Live: 0 Live: 0 – – 200%; 200%; � � Critical levels < 100 % Critical levels < 100 % - - half of the normal relative moisture half of the normal relative moisture
Fuels: RAWS Data availability -real time -set for models
Fuels and Fire Hazards Fuels and Fire Hazards � Wildland Fuels are divided into 4 classes: Wildland Fuels are divided into 4 classes: � Ground Ground � Duff Duff – – moist upper A horizon, decomposing litter moist upper A horizon, decomposing litter � Not a big player in fire behavior Not a big player in fire behavior � Surface Surface � All dead downed woody stuff, litter, grasses, herbs, shrubs All dead downed woody stuff, litter, grasses, herbs, shrubs � Ladder Ladder dd dd � Fuels that provide vertical continuity from Surface to Crown Fuels that provide vertical continuity from Surface to Crown � Crown Crown � Overstory biomass Overstory biomass � Reductions of these fuels limit fire intensities Reductions of these fuels limit fire intensities � Fuel treatments! Fuel treatments! � Surface Surface – – Ladder Ladder - - Crown Crown
Fire Behavior Fire Behavior � 3 Interacting classes of influencing variables: 3 Interacting classes of influencing variables: � � Fuels Fuels � Topography Topography � We ther � Weather We ther Weather
Fuels Fuels � Already got it… Already got it… �
Topography Topography � Slope Slope � Fires on slopes can Fires on slopes can � Increase flame length, Increase flame length, � Preheat upslope fuels Preheat upslope fuels � These can increase intensity and rate These can increase intensity and rate- y -of of-spread spread p p � Terrain Terrain � Topography can influence: Topography can influence: � Slope (!) Slope (!) � Diurnal air movement Diurnal air movement � Aspect: fuels temperatures Aspect: fuels temperatures � Physiography: Physiography: � Chimneys, saddles, box canyons Chimneys, saddles, box canyons
Chimney, slopes: NOT a good place to continue standing
Weather Weather � Temperature Temperature � Relative Humidity Relative Humidity � Precipitation Precipitation � Atmospheric stability Atmospheric stability � Vertical stability (inversions), advection Vertical stability (inversions), advection � Winds & Windspeed � Winds & Windspeed Winds & Windspeed Winds & Windspeed � General General – – broad scale pressure gradients broad scale pressure gradients � Foehn Winds: Santa Anas, Diablos Foehn Winds: Santa Anas, Diablos � Local Local � Sea breezes, land breezes, slope winds Sea breezes, land breezes, slope winds � Fire Whorls Fire Whorls � Critical: weather can change rapidly, changing fire behavior Critical: weather can change rapidly, changing fire behavior rapidly rapidly
Whorls: 10 to 1000’s m 2 , increase intensity eight-fold Weather Weather
Weather Weather � Thunderstorms Thunderstorms � � Violent Violent up/downdrafts up/downdrafts � Lightning Lightning � Sometimes associated S S Sometimes associated i i i i d d with cold fronts with cold fronts � Downdrafts often lead Downdrafts often lead to violent, lateral front to violent, lateral front winds winds
Fire Movement Fire Movement � 4 Processes: Convection, Conduction, Radiation, 4 Processes: Convection, Conduction, Radiation, � Mass Transfer Mass Transfer � Convection: Convection: � Conduction is the transfer of thermal energy (Q) from a � Conduction is the transfer of thermal energy (Q) from a Conduction is the transfer of thermal energy (Q) from a Conduction is the transfer of thermal energy (Q) from a region of higher temperature (A) to a region of lower region of higher temperature (A) to a region of lower temperature via direct molecular communication between temperature via direct molecular communication between mediums in direct physical contact without a flow of the mediums in direct physical contact without a flow of the material medium material medium
Convection Convection � a mechanism of heat transfer occurring because a mechanism of heat transfer occurring because � of bulk motion (observable movement) of fluids of bulk motion (observable movement) of fluids � Air is a fluid… Air is a fluid…
Radiation Radiation � Thermal radiation Thermal radiation is electromagnetic is electromagnetic radiation emitted radiation emitted from the surface from the surface of an object of an object which is due to which is due to the object's the object's temperature. temperature. � Infrared radiation Infrared radiation Colorado DNR
Mass Transfer Mass Transfer � Phrase commonly used for physical processes Phrase commonly used for physical processes � that involve molecular and convective transport that involve molecular and convective transport of atoms and molecules within physical systems: of atoms and molecules within physical systems: � Moving stuff (usually gaseous) by convection � Moving stuff (usually gaseous) by convection Moving stuff (usually gaseous) by convection Moving stuff (usually gaseous) by convection � Molecules Molecules � Sparks (glowing embers) Sparks (glowing embers)
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